The present invention relates to the treatment and prevention of bacterial wilt in plants resulting from Ralstonia Solanacearum infestation. More particularly, the present invention relates to the prevention and treatment of bacterial wilt in crops by treatment with 3-(3-indolyl) butanoic acid.
Ralstonia solanacearum (hereinafter Ralstonia) is the bacteria responsible for the extremely destructive disease in potatoes, tomatoes, tobacco, eggplant, bell peppers, peanuts and related crops commonly known as bacterial wilt. Bacterial wilt is also known regionally as southern bacterial wilt, brown rot, slime disease and mattery eye. Bacterial wilt is often first observed in plants when one or more leaves droop during the heat of the day. As the disease progresses, all the leaves of the plant may droop. Eventually, the entire plant falls to the ground, its transpiration system choked by milky white bacterial colonies.
Ralstonia, the bacteria responsible for bacterial wilt, is a gram-negative short rod bacteria. The disease progresses as the Ralstonia bacteria plug the vessels of the infected plantsxe2x80x94especially the xylemxe2x80x94disrupting the systemic flow of fluids in the plants. This disruption prevents the transport of nutrients throughout the plants and stops the transpiration of water and gases upwards through the plant. As fluids above the blocked areas are transpired away, the structural support of the plants dissipates. The presence of the disease is confirmed by cutting a section of the stem and suspending it in waterxe2x80x94if milky white strands are seen oozing from the plant""s vascular system into the water, then Ralstonia is likely the source of the disease.
Ralstonia has been characterized as one of the most serious bacterial diseases of potatoes in the warm regions of the world. One of the reasons that worldwide potato production is so vulnerable to bacterial wilt is due to its transmission as a latent infection in seed potatoes. While quarantine measures have been used to avoid spread of the disease by restricting the production of the seed potatoes, this affects the economy in the quarantine regions.
Attempts are also made to control bacterial wilt by crop rotation. This method is not completely satisfactory for a number of reasons. Most problematic is that Ralstonia bacteria may remain in the soil, so that future outbreaks of bacterial wilt cannot be totally avoided by crop rotation alone. In addition, crop rotation can force growers to plant less preferred crops, affecting both public supply of the rotated crop and grower profitability when less desirable crops grown.
Research is currently underway in Europe with the aim of developing a transgenic potato resistant to Ralstonia. However, such a product has not yet been developed, and even if developed, public acceptance of such a product cannot be predicted.
Although the Consultative Group on International Agricultural Research has recently concluded that appropriate chemical control measures that are practical and effective do not exist, U.S. Pat. No. 6,015,830 to MATSUDA, et al., for ANTIBACTERIAL COMPOUNDS FOR RALSTONIA SOLANACEARUM, which issued Jan. 18, 2000, discloses that antibacterial compounds comprising substantially (S)-3-(3-indolyl) butanoic acid can selectively inhibit the growth of Ralstonia. Experiment Part 4 of U.S. Pat. No. 6,015,830 describes the cultivation of Ralstonia bacteria in a physiological brine, in which the extent of Ralstonia colonization is determined by measuring the turbidity of the culture liquid. After an (S)-3-(3-indolyl) butanoic acid solution is added to the culture liquid, turbidity is further measured. An increase in turbidity is treated as indicative of continued Ralstonia growth. The absence of change in turbidity is treated as indicative of suppression of Ralstonia growth. This patent does provide evidence of suppression of Ralstonia growth after the addition of an (S)-3-(3-indolyl) butanoic acid solution. While the patent abstract concludes that bacterial wilt is suppressed dependably, the experiments described in the patent do not describe with any particularity an enabling treatment for growing plants challenged by bacterial wilt.
Experimental use of 3-(3-indolyl) butanoic acid (hereinafter 3-IBA) in hydroponic solutions in which tomato plants are grown is described in xe2x80x9cControl of the Bacterial Wilt of Tomato Plants by a Derivative of 3-Indolepropionic Acid Based on Selective Actions on Ralstonia solanacearumxe2x80x9d, by K. Matsuda, et al., J. Agri. Food Chem., 1998, 46, pp. 4416-19. Control of the bacterial growth by 3-IBA in a hydroponic culture of tomato plants is evaluated by first inoculating a hydroponic culture medium with Ralstonia on day 0, adding 3-IBA on day 1, transferring month-old tomato plants to the culture on day 2, and counting the numbers of wilted plants on each day thereafter. The report concludes that in the absence of the 3-IBA, wilt is observed in more than 60% of the plants transferred into hydroponic solutions, while less than 10% of the plants transferred into hydroponic solutions previously treated with 3-IBA are slightly wilted.
While the results reported above are indeed heartening, it is not clear whether the successful suppression of Ralstonia growth in hydroponic solutions prior to tomato plant transfer has direct applicability to soil grown crops. This is because it cannot be ascertained from the information given, whether the 3-IBA effectively suppressed Ralstonia growth prior to the introduction of the tomato plants, so that the hydroponic solution transpired by the transferred tomato plants contained not only well-dispersed Ralstonia bacteria but also an equally well-dispersed concentration of 3-IBA. In the absence of such a ubiquitous medium, it is not known whether plants infected with Ralstonia bacteria, having already lost some transpiration capability, can effectively transport 3-IBA applied to the soil, upward through the partially or wholly plugged xylem, to where Ralstonia bacteria are colonizing.
It is against this background that the significant improvements and advancements of the present invention have taken place.
A method of preventing and treating bacterial wilt in crops by foliar application of 3-(3-indolyl) butanoic acid is disclosed. Although the preferred optical isomer for inclusion in the compositions of the present invention and foliar application of such compositions, is the (S)-3-(3-indolyl) butanoic acid isomer, use of racemic mixtures of the (S) and (R) isomers are contemplated.